Abstract: A method of transmitting signals on a cable comprises filtering the signals at a transmitter to compensate for nonuniform frequency response of the cable at a maximum cable length, and clipping the signals at a receiver when the filtering results in overshoot of a signal level by the signals.

Abstract: There is disclosed a digital filter cell capable of processing in a first mode a first signal having real data components only and processing in a second mode a second signal having real data components and imaginary data components. The digital filter cell comprises: 1) a plurality of serially coupled coefficient registers for receiving a sequence of coefficients; 2) a plurality of serially coupled data registers for receiving a sequence of digital data samples, each register having a tap output; 3) a data multiplexer having a plurality of input channels for receiving the tap outputs from the plurality of serially coupled data registers; and 4) a product summation circuit having a first input coupled to an output of the data multiplexer and a second input coupled to an output of a selected one of the plurality of serially coupled coefficient registers.

Abstract: A switching amplifier is described which includes an input stage having a first node associated therewith and a power stage having a second node associated therewith. An actual loop delay is defined with reference to the first and second nodes. Delay detection circuitry compares the actual loop delay to a reference loop delay. A dynamic delay line controlled by the delay detection circuitry controls the actual loop delay to correspond to the reference loop delay.

Abstract: An equalizer according to the present invention includes a plurality of switch elements for selecting output data from the delaying elements in response to the odd and even clock signals. The odd and even clock signals are, in time division mode, produced by the system clock signal which is faster than a symbol clock signal. The present invention can reduce the number of multipliers. For example, a convolutional operating part of the equalizer having N flip-flops as a delaying element, only N/2 multipliers are needed.

Abstract: A method and apparatus to accomplish fast adaptive equalization of a wireless communication channel is disclosed. The equalization method and apparatus utilize time varying adaptive filter coefficients and time varying convergence parameters in a fast adaptive algorithm to provide fast channel equalization in a wireless communication system.

Abstract: An arrangement is described for the equalization of a frequency signal, the arrangement including a channel filter and an equalizer connected downstream of the channel filter, for a satellite communication system in particular. The equalizer is an at least partially superconductive reflection equalizer.

Abstract: At least two innovations are used to overcome the limitations of conventional transimpedance or high impedance optical receiver front end amplifiers. The innovations are a) multiple stage equalization of a high-feedback resistor, low-gain transimpedance amplifier to obtain high sensitivity, and b) range switching of feedback resistors and equalization capacitors to obtain high overload. With these approaches, it is possible to design an optical receiver operating at the intrinsic limits of available device technology.

Abstract: Outputs from respective elements of an array antenna 21 are demodulated, and the demodulated outputs are stored in storage means 29. The demodulated outputs are multiplied by tap coefficients of adaptive array antenna, then the multiplied outputs are combined by combining means 28, and the combined output is provided via a feed forward filter 22 to an adaptive equalizer 23, wherein it is equalized to obtain a decision symbol. During reception of a training signal the tap coefficients of adaptive array antenna and tap coefficients of the adaptive equalizer 23 are subjected to convergence processing by tap coefficient calculating means 24 so that an error signal becomes small, and then tap coefficients of the feed forward filter 22 and the adaptive equalizer 23 are subjected to convergence processing by tap coefficient calculating means 25 so that an error signal becomes small.

Abstract: An apparatus and method for equalizing the characteristics of a communication channel in a computer extension system. A time measurement system determines the delay time in a pair of wires connecting a computer at a first site to peripherals at a second site. The value of the delay time serves as control signal to select filters where the filters have inverse channel frequency characteristics.

Abstract: To provide a method of pseudogrounding which is capable of protecting against EMI by pseudogrounding communication lines, etc. without necessity of expensive ferrite cores and increasing the number of steps and cost. A wiring which is connected to an LSI (43) on a package and is connected to an external wiring (47) via a connector (461), radio-frequency connected via a capacitance (451, 452) to ta housing (42) in which protection against EMI is achieved so that the radiated noise energy is not higher than EMI restricted value level. This enables said wiring to be pseudogrounded.

Abstract: Described is an attenuation equalizer for compensating an attenuation characteristic of a transmission line, including a first node and a second node, a first frequency filter unit coupled to the first node and/or to the second node for frequency filtering an applied signal, a first current source coupled to the first node in order to control a current provided by the first current source to the second node.

Abstract: An xDSL communication system having a reduced number of digital filter coefficients. The full-length equalizer channel impulse response is truncated by first selecting a subset of contiguous filter samples followed by windowing and convolution with a time domain representation of a frequency domain filter. The result is a shorter equalizer having fewer coefficients so as to improve data transmission rate.

Abstract: Disturbances in a bipolar signal in the case of large line lengths are suppressed. The signal is led to a coarse setting and a fine setting in an equalizer and to a downstream level detector. From there it is fed back to the equalizer via a control device. Sampling is performed in this case with the aid of a measuring clock pulse. The sampling clock pulse is dimensioned such that undersampling is carried out. Three reference levels are used, from which one digital sampled signal is derived in each case. A coarse setting or fine setting is initiated as a function of a percentage-prescribed number of upper and lower threshold violations.

Abstract: A low cost and low power adaptive cable equalizer that is particularly suitable for fast Ethernet data communication is disclosed. According to various embodiments of the present invention, first and second order adaptive equalizers are implemented using CMOS continuous-time analog signal processing, with variable resistors, linear capacitors and high-speed operational amplifiers.

Abstract: A network line equalizer is provided in combination with a compensation circuit. The network line equalizer includes first and second nodes, first and second current sources respectively connected to the first and second nodes, first and second transistors respectively connected also to the first and second nodes with a gate of the first transistor receiving a first signal of a differential pair of transmitted signals and a gate of the second transistor receiving a second signal of the differential pair of transmitted signals, a third transistor connected between the first and second nodes, and a control line connected to a gate of the third transistor.

Abstract: A method and apparatus for providing equalization for a communication channel is provided. The invention uses edge transition samples, such as those obtained for phase detection in a phase locked loop (PLL) circuit, to determine the amount of equalization to be applied to signals received from a communication channel. By monitoring run lengths of consecutive identical bits received from the communication channel, the invention provides equalization for various frequency components present in the receive signal. One embodiment of the invention subtracts a weighted RC-filtered version of the receive signal from the unfiltered receive signal to provide an equalized receive signal. In this embodiment, a control circuit that monitors the received run lengths and edge transition information adjusts the resistance of the RC filter to adapt the equalization to the data being received and the potentially time varying conditions for the communication channel.

Abstract: An equalization device has a digital equalizer for joint tuning of a data-carrying signal distorted by analog transmission. The digital equalizer includes a closed-loop automatic gain control (AGC) circuit for applying a compensatory frequency-independent gain to the distorted signal followed by a frequency filter for applying a compensatory frequency-dependent gain to the signal. Joint tuning produces an output signal which more closely resembles the originally transmitted signal, facilitating recovery of implicit clock and more reliable data recovery. The digital equalizer may be advantageously stage-implemented as a preliminary digital equalizer which is preceded by an analog equalizer and followed by a final digital equalizer.

Abstract: A system and method for applying channel weights in a communication system are presented. The application of weights derived from a sample window is time-shifted into that sample window, decreasing the effects of channel variation and partially compensating for degradation due to differential detection.

Abstract: A method and apparatus for equalizing the frequency response of a transmission line is provided. The method includes the steps of modelling the frequency response of the transmission media for a predetermined frequency range to a predetermined accuracy; determining a desired equalizer response by taking an inverse of the modelled frequency response of the first step; implementing an equalizer that exhibits the desired response; and utilizing the equalizer to equalize the frequency response of the transmission line. The apparatus includes an adaptive equalizer circuit which includes a plurality of signal processor circuits which each take an input signal from the transmission line and process it to mimic a term in a transfer function which represents an inverse of the transfer function of the transmission line. The signals from these processors are then summed and multiplied by a programmable gain term. Then the input is added to the output of the multiplier to form an output equalizer signal.

Abstract: In a receiver for signals in a multilevel partial response class-IV communication system, the coefficients of a digital adaptive equalizer need to be updated to minimize the error due to noise and signal distortion. After initial convergence of the equalizer coefficients to near-optimum settings, an estimate of the mean-square error gradient for coefficient updating can be obtained in decision-directed mode from an estimate of the error signal. In the absence of a reference signal, initial convergence must be achieved in self-training mode. The decision-directed error signal is then replaced by a pseudo-error signal for the computation of an approximation of the mean-square error gradient. The invention provides a particular self-training procedure which outperforms known methods in terms of speed of convergence and achieved mean-square error values, and does not require timing recovery prior to equalizer convergence.

Abstract: An adaptive equalizer is implemented using digital feedback control and using jitter as the adjustment criteria. An adjustable transfer function is implemented to equalize an input signal to enhance the frequency response of the associated system. Jitter is determined for the filtered signal, and the frequency response of the transfer function is varied accordingly by applying a digital adjustment signal to the transfer function structure (for example, a lead-lag filter). The adaptive equalizer can thereby adapt to various transmission medium lengths and signal degradation levels.

Abstract: An adaptive cable equalizer is provided with a simple architecture, wherein a single control structure: controls the adaptation of the filter for compensating for cable length while simultaneously compensating for process and temperature variations; optimizes the SNR at any cable length by controlling biasing current sources; and uses a two-stage architecture which eliminates start-up problems and optimizes output levels to obtain optimal dc restoration while simultaneously allowing for independent optimization of the output levels of the recovered data in accordance with other requirements as desired. An analog adaptive equalizing filter is used for accurately synthesizing the inverse transfer function of cables of variable lengths. Data rates up to and beyond 400 Mbps are supported and the adaptive behavior automatically compensates for different cable lengths as well as process variations (with respect to the process(es) used for fabricating the equalizer in a monolithic form) and temperature variations.

Abstract: A method and apparatus for equalizing a communications signal transmitted through a transmission medium includes an integrated continuous-time filter and circuitry for developing a feedback signal to compensate for distortion in the signal caused by the transmission medium. The control signal adjusts the transfer characteristics of the integrated continuous-time filter thereby compensating for loss and distortion of the signal caused by the transmission medium and further tunes the integrated continuous-time filter thereby compensating for semiconductor process variations in the integrated continuous-time filter.

Abstract: A method is described for producing coefficient leakage in an adaptive filter/equalizer without the need for using an adder/subtractor for each coefficient. Specifically, a method is provided for incrementally reducing the magnitude of one or more coefficients in an adaptive filter/equalizer solely through a defined manipulation of certain bits in that coefficient, such bit manipulation being carried out on a periodic basis. The period for such bit manipulation will generally track the frequency of adaptation iteration for such a filter/equalizer.

Abstract: The object of the present invention is to provide an automatic equalizer which can automatically equalize distortion including a precursor component with a small amount of calculation and a small circuit scale.

Abstract: An auto-coefficient renewal digital channel equalizer is disclosed, including an auto-coefficient renewing device for automatically renewing a coefficient using received data and an error signal, an error detecting device for detecting an error signal from a signal of the auto-coefficient renewing device, a device for determining convergence or divergence of the error signal detected in the error detecting device to produce a convergence or divergence signal according to a result of the determination, and an error processing device for shifting down the error signal detected in the error detecting device a certain number of bits in response to a convergence signal to produce a signal smaller than the received error signal to the auto-coefficient renewing device, thereby processing the coefficient renewal at the same rate with the data for all of the taps of an equalizer. The equalizer converges at an increased rate, and operation of the equalizer is made more stable even in diversion of a reception channel.

Abstract: The analog adaptive equalizer provides convergence of an error signal by decoupling the error canceller, the automatic gain control and the filter to provide truly adaptive error minimization. The invention includes an automatic gain control (AGC) circuit for providing broadband amplification of an input signal to generate an AGC output signal, a filter for receiving the AGC output signal and providing high frequency signal conditioning to generate a filter output signal, an error detection circuit for generating an error signal representing the difference between the filter output signal and an expected output signal and a calculator for receiving the error signal and providing a gain correction signal to the automatic gain circuit to adjust the gain of the automatic gain circuit and a filter control signal to adjust the filter range of the filter, the gain correction signal and the filter control signal being used to cancel the error signal.

Abstract: An integrated circuit includes a single pole double throw switch including a transmitting and receiving port, a transmitting port, and a receiving port. A transmission switch is coupled between the transmitting port and the transmitting and receiving port. A reception switch is coupled between the receiving port and the transmitting and receiving port. The reception switch includes a field effect transistor having a gate, a drain and a source. A voltage generating circuit receives first and second power supply voltages. The first power supply voltage is greater than the second power supply voltage. The voltage generating circuit generates a third voltage lower than the second power supply voltage and applies the third voltage to the gate of the field effect transistor of the reception switch during transmission.

Abstract: An adaptive equalizer for adaptively equalizing a data signal received via a communications path having a signal loss magnitude which increases with signal frequency includes multiple, serially coupled adaptive filter stages. The input data signal is successively filtered and magnitude weighted by successive adaptive filter circuits in accordance with corresponding, respective adaptation control signals. The frequency domain ratio of output signals to corresponding input signals for each adaptive filter circuit represents a corresponding, respective adaptive filter transfer function. An equalizer controller, in accordance with a single equalization control signal, generates the multiple, individual adaptation control signals.

Abstract: A cable length estimation circuit for receiving an input MLT-3 signal provided through an arbitrary length cable and providing a control signal to an equalizer indicating the estimated length of the cable enabling the equalizer to compensate for distortion of the MLT-3 signal resulting from the cable. The cable length estimation circuit includes an edge rate detection circuit for measuring the rate of change in voltage with respect to time during transitions of the MLT-3 signal to provide an indication of cable length. The cable length estimation circuit can also include a digital averaging circuit which provides an average value for signals from the edge rate detection circuit for a desired number of transitions of the MLT-3 signal. The cable length estimation can also include a baseline wander detection circuit which functions so that previous cable length estimations are provided when baseline wander is detected.

Abstract: An equalizer receives an analog input signal and filters the signal to undistort the input signal. A converter stage converts the analog input signal into a digital output signal for use in a digital system. A bit sequence indicator analyzes the structure of the digital output signal to determine whether any errors have occurred in transmission and conversion. An adaptor state machine causes the modification of the analog signal based on a feedback loop including information on the errors detected in the packets of digital signals, rather than the analog data itself.

Abstract: A device (1) for correcting the amplitude/frequency characteristic of an input signal (FI), particularly from transmission cables (40), having a minimal frequency f1, a center frequency f0 and a maximal frequency f2, the input signal (FI) having an attenuation as a function of frequency characteristic that increases between f1 and f2, the correction device (1) supplying a corrected output signal (). The correction device includes two cascaded filters (41, 42), the first of the filters receiving the input signal (FI) and supplying a filtered signal (SFI) to the second of the filters, the second of the filters supplying the corrected output signal (). One of the filters is a band-stop filter (41) having a center frequency f3 less than or equal to f1, the other of the filters being a band-pass filter (42) having a center frequency f4 greater than or equal to f2. The center frequencies f3 and f4 satisfy the equation:f3.times.f4=f0.sup.

Abstract: An automatic line equalizer for use with a T1 or an E1 repeater in a telecommunications system is disclosed. The equalizer includes a first equalizing means for equalizing an input line having a line length falling within a first range and a second equalizing means for equalizing an input line having a line length falling within a second range. The equalizer includes a line condition/length detector. The equalizer includes switch means for selectively coupling one of the first and second equalizers to the selected input line as a function of a line condition indication. The switching means prevents hunting between said first and said second equalizers.

Abstract: An adaptive cable equalizer (10) includes an input section (12) that receives a radio frequency electrical signal from a cable (14). The input section (12) provides the electrical signal to an equalizing amplifier section (16) that controls an amount of current flow of the electrical signal to an equalizing controller (18). The equalizing controller (18) generates an equalized output signal (21) through a voltage drop which is proportional to a roll-off distortion of the cable (14). The voltage drop is processed by an amplifier (80) and a line receiver (88) to reconstruct the electrical signal in a digital representation of the equalized output signal (21). The voltage drop is also fed to a detector (20) that generates a control signal (23) and a bias signal (25) to adjust the conductivity of the equalizing amplifier section (16). In this manner, adjustments are automatically made in order to provide the equalized output signal (21) regardless of the characteristics of the cable (14).

Abstract: A cellular communication system having all of its components operating under a single system control unit is provided so that the various components of the system can be adjusted as the parameters of the other components or the dynamic characteristics of the cellular channel change.

Abstract: An adaptive equalization method and device which provides for the equalization of symbol sequences sent through fading multipath channels with time and frequency dispersion. By using a trainer system to supply an estimate of the received symbol sequence to a trainee system, equalization of the received symbol sequences is accomplished without the need for training sequences and with the ability of compensating for spectral nulls without a substantial increase in the noise in the system. The trainer system is configured as a decision directed equalizer with a feed forward filter having the received symbol sequence as input and connected to a decision element that outputs decided symbols. The trainee system is similar to decision feed back equalization in that it has a feed forward filter, a feedback filter and a decision element but, differs in that the input to the feed back filter is provided by the trainer system. The feed forward filter of the trainee system takes received symbol sequence as input.

Abstract: In a decision feedback equalizer, symbols from an array of antennas are fed to a first filter where they are respectively multiplied with first weight coefficients and supplied to a combiner where they are combined with second symbols to produce a combined symbol. A decision circuit makes a decision on the combined symbol and produces a decision symbol. Decision symbols successively generated by the decision circuit are fed to a second filter where they are respectively multiplied with second weight coefficients and supplied to the combiner as the second symbols. A difference between the decision symbol and the combined symbol is detected to produce a decision error.

Abstract: An adaptive equalizer decision circuit for a digital television signal, including a field synchronizing signal, consisting of multilevel symbols and a DC offset representing a pilot. The variation of the DC level of the received signal during the field sync with respect to a predetermined threshold is derived for placing the equalizer in a training signal or data directed operating mode. Another approach determines the difference between a current value of the field sync and each of a plurality of values of the field sync in previous fields and determining therefrom whether the equalizer should be in its data directed mode of operation or in its training signal mode of operation. A modification consists in controlling the step size of the equalizer based upon either the DC level variation or the field sync differences of the received signal. The modification may be used alone or in combination with the equalizer operating mode control.

Abstract: An analog, adaptive generalized transversal equalizer for use in the filtering system of a disc drive PRML read channel, the transversal equalizer employing the use of non-ideal delay elements. The filtering system comprises the equalizer connected in series with an adaptive, analog prefilter. The prefilter is comprised of a plurality of serially connected, adaptive, analog filter stages having variable transfer functions determined by adaptive parameter signals received by the filter stages. The generalized transversal equalizer comprises a plurality of serially connected, adaptive, analog low pass filters, having taps on either side of each low pass filter, a plurality of multipliers that receive signals at the tap locations of the delay circuit, and a summing circuit that receives the outputs of the multipliers.

Abstract: An equalizer circuit for equalizing waveform distortion of a signal that propagates through a lossy transmission cable connected between a receiver and a transmitter, the equalizer circuit including a plurality of equalizer units which are connected in series with one another and a plurality of taps, each tap providing a different equalized representation of a signal being transmitted through the transmission cable to which the equalizer circuit is connected, and a control circuit for determining the tap at which appears an equalized signal that exhibits minimum error relative to the transmitted signal, the determination being made by applying an envelope detector to each tap for obtaining low frequency envelope signals for the signal appearing at each tap and for comparing the low frequency envelope signals thus obtained with a common DC reference signal that is related to the ideal transmitted signal amplitude.

Abstract: An automatic equalizer comprises an adaptive matched filter (AMF) and a decision feedback equalizer (DFE), which is designed to stop operation of minus taps of the AMF while a demodulator is in synchronous status and to enable the minus taps of the AMF while it is in asynchronous status.

Abstract: An IQ modulator incorporates a quadrature network that is responsive to a frequency dependent control signal and that has in-phase and quadrature signals that are of equal amplitude and in exact quadrature over a wide range of applied frequencies. The quadrature network includes RC and CR phase shifters whose C's are fixed capacitors of equal value and whose R's are made equal to each other and to the capacitive reactance of the C's by the action of the frequency dependent control signal. The R's may be FET's. The frequency dependent control signal may be generated without express knowledge of the applied frequency by a servo loop that nulls out the amplitude difference between the in-phase and quadrature outputs from the quadrature network; it may also be generated from a look-up table as an express function of frequency. The frequency dependent control signal is split into separate instances that are applied to each R, and an offset may be introduced therebetween to provide extreme precision.

Abstract: An improved adaptive three tap transversal equalizer for partial-response signaling. The invention reduces the complexity of the hardware, as well as reducing the sensitivity of the equalizer to gain and timing errors. The present invention employs an algorithm based on sample values around zero. The resulting decrease in average magnitude of the error results in decreased sensitivity to gain errors. The algorithm of the present invention improves cancellation of sample timing errors. In the present invention, the coefficient of an adaptive cosine equalizer is updated by integration of a stochastic gradient. To calculate the gradient, the product of the quantized output from the previous sample and the output from the present sample is summed together with the product of the output from the previous sample and the quantized output from the present sample. In addition, the equalizer output is masked such that values quantizing to non-zero values are discarded in the update algorithm.

Abstract: The present invention includes a method and system for controlling an equalizer equalizing data transmitted a communications channel which is oversampled at an oversampling rate of M. The method of the present invention includes the steps of initializing a plurality of data pointers and a first buffer stored in an input memory (22); generating a buffer full flag in response to filling the first buffer with a pre-determined number of data samples; initializing a counter (28) in response to the buffer full flag, the counter (28) generating an enable signal every M cycles; equalizing a portion of the pre-determined number of data samples in response to the enabling signal using an equalizer (20), where the portion of the pre-determined number of data samples is located using the plurality of data pointers; and adjusting the plurality of data pointers in response to the equalizing step using an FSE controller (24).

Abstract: The invention provides an automatic equalizer which can keep, even where it is employed for a modem which has a very large number of taps, a high degree of accuracy in error correction of tap coefficients and can obtain an equalized signal with a high degree of accuracy. The automatic equalizer includes an equalization calculation section including a plurality of delaying sections, a tap coefficient multiplication section and a totaling calculation section, a tap coefficient error correction section for correcting errors of tap coefficients for the equalization calculation section based on an input to the automatic equalizer and an output of the automatic equalizer, and an input level setting section for setting an input signal level to the equalization calculation section and an input signal level to the tap coefficient error correction section to levels different from each other.

Abstract: In an equalizer including a plurality of delay elements, a plurality of weighting elements and an adder, the impulse response of a signal transmission channel is estimated to selectively switch over a plurality of selector switches associated with the inputs and outputs of the respective delay elements, thereby selectively changing the combination of the delay elements and the weighting elements transmitting an input signal from the channel to the adder and also changing the combination of the adder and a delay element feeding back the output of the discriminator to the adder. Thus, the number of required taps of the equalizer can be reduced, so that the power consumption and size of the equalizer can be reduced.

Abstract: A method and apparatus for a decision-directed timing recovery scheme to stabilize its equalizer positioning by centering equalizer taps is disclosed. First, the measure of equalizer positioning is calculated. The measure is then scaled to generate a timing bias signal. The timing bias signal is used to shift the timing phase of the equalizer input.

Abstract: A multistate electronic transfer standard provides electronic conditions to at least one of two ports of a vector network analyzer. One embodiment of the multistate electronic transfer standard includes a plurality of semiconductor interconnected by transmission lines. Each of the semiconductor devices are biased to generate different conditions at each of the two ports. A control computer controls the biasing of devices according to a predetermined procedure and compares impedance values measured for at least one of the two ports of the network analyzer to known values stored by the control computer. The control computer thereby derives calibration coefficients that are used by the network analyzer in performing further measurements.

Abstract: An adaptive equalization method and device which provides for the equalization of symbol sequences sent through fading multipath channels with time and frequency dispersion. By using a trainer system to supply an estimate of the received symbol sequence to a trainee system, equalization of the received symbol sequences is accomplished without the need for training sequences and with the ability of compensating for spectral nulls without a substantial increase in the noise in the system. The trainer system is configured as a decision directed equalizer with a feed forward filter having the received symbol sequence as input and connected to a decision element that outputs decided symbols. The trainee system is similar to decision feed back equalization in that it has a feed forward filter, a feedback filter and a decision element but, differs in that the input to the feed back filter is provided by the trainer system. The feed forward filter of the trainee system takes received symbol sequence as input.

Abstract: A multistate electronic transfer standard provides electronic conditions to at least one of two ports of a vector network analyzer. One embodiment of the multistate electronic transfer standard includes a plurality of semiconductor interconnected by transmission lines. Each of the semiconductor devices are biased to generate different conditions at each of the two ports. A control computer controls the biasing of devices according to a predetermined procedure and compares impedance values measured for at least one of the two ports of the network analyzer to known values stored by the control computer. The control computer thereby derives calibration coefficients that are used by the network analyzer in performing further measurements.